2 files changed, 273 insertions, 106 deletions

diff --git a/editors/code/src/inlay_hints.ts b/editors/code/src/inlay_hints.ts
index 08d3a64a7..bbe8f67ef 100644
--- a/editors/code/src/inlay_hints.ts
+++ b/editors/code/src/inlay_hints.ts
@@ -1,156 +1,323 @@
+import * as lc from "vscode-languageclient";
 import * as vscode from 'vscode';
 import * as ra from './rust-analyzer-api';
 
 import { Ctx } from './ctx';
-import { log, sendRequestWithRetry, isRustDocument } from './util';
+import { sendRequestWithRetry, assert } from './util';
 
 export function activateInlayHints(ctx: Ctx) {
-    const hintsUpdater = new HintsUpdater(ctx);
+    const hintsUpdater = new HintsUpdater(ctx.client);
+
     vscode.window.onDidChangeVisibleTextEditors(
-        async _ => hintsUpdater.refresh(),
+        visibleEditors => hintsUpdater.refreshVisibleRustEditors(
+            visibleEditors.filter(isRustTextEditor)
+        ),
         null,
         ctx.subscriptions
     );
 
     vscode.workspace.onDidChangeTextDocument(
-        async event => {
-            if (event.contentChanges.length === 0) return;
-            if (!isRustDocument(event.document)) return;
-            await hintsUpdater.refresh();
+        ({ contentChanges, document }) => {
+            if (contentChanges.length === 0) return;
+            if (!isRustTextDocument(document)) return;
+
+            hintsUpdater.refreshRustDocument(document);
         },
         null,
         ctx.subscriptions
     );
 
     vscode.workspace.onDidChangeConfiguration(
-        async _ => hintsUpdater.setEnabled(ctx.config.displayInlayHints),
+        async _ => {
+            // FIXME: ctx.config may have not been refreshed at this point of time, i.e.
+            // it's on onDidChangeConfiguration() handler may've not executed yet
+            // (order of invokation is unspecified)
+            // To fix this we should expose an event emitter from our `Config` itself.
+            await hintsUpdater.setEnabled(ctx.config.displayInlayHints);
+        },
         null,
         ctx.subscriptions
     );
 
     ctx.pushCleanup({
         dispose() {
-            hintsUpdater.clear();
+            hintsUpdater.clearHints();
         }
     });
 
-    // XXX: we don't await this, thus Promise rejections won't be handled, but
-    // this should never throw in fact...
-    void hintsUpdater.setEnabled(ctx.config.displayInlayHints);
+    hintsUpdater.setEnabled(ctx.config.displayInlayHints);
 }
 
-const typeHintDecorationType = vscode.window.createTextEditorDecorationType({
-    after: {
-        color: new vscode.ThemeColor('rust_analyzer.inlayHint'),
-        fontStyle: "normal",
-    },
-});
 
-const parameterHintDecorationType = vscode.window.createTextEditorDecorationType({
-    before: {
-        color: new vscode.ThemeColor('rust_analyzer.inlayHint'),
-        fontStyle: "normal",
-    },
-});
+const typeHints = {
+    decorationType: vscode.window.createTextEditorDecorationType({
+        after: {
+            color: new vscode.ThemeColor('rust_analyzer.inlayHint'),
+            fontStyle: "normal",
+        }
+    }),
 
-class HintsUpdater {
-    private pending = new Map<string, vscode.CancellationTokenSource>();
-    private ctx: Ctx;
-    private enabled: boolean;
+    toDecoration(hint: ra.InlayHint.TypeHint, conv: lc.Protocol2CodeConverter): vscode.DecorationOptions {
+        return {
+            range: conv.asRange(hint.range),
+            renderOptions: { after: { contentText: `: ${hint.label}` } }
+        };
+    }
+};
+
+const paramHints = {
+    decorationType: vscode.window.createTextEditorDecorationType({
+        before: {
+            color: new vscode.ThemeColor('rust_analyzer.inlayHint'),
+            fontStyle: "normal",
+        }
+    }),
 
-    constructor(ctx: Ctx) {
-        this.ctx = ctx;
-        this.enabled = false;
+    toDecoration(hint: ra.InlayHint.ParamHint, conv: lc.Protocol2CodeConverter): vscode.DecorationOptions {
+        return {
+            range: conv.asRange(hint.range),
+            renderOptions: { before: { contentText: `${hint.label}: ` } }
+        };
     }
+};
+
+class HintsUpdater {
+    private sourceFiles = new RustSourceFiles();
+    private enabled = false;
 
-    async setEnabled(enabled: boolean): Promise<void> {
-        log.debug({ enabled, prev: this.enabled });
+    constructor(readonly client: lc.LanguageClient) { }
 
+    setEnabled(enabled: boolean) {
         if (this.enabled === enabled) return;
         this.enabled = enabled;
 
         if (this.enabled) {
-            return await this.refresh();
+            this.refreshVisibleRustEditors(vscode.window.visibleTextEditors.filter(isRustTextEditor));
         } else {
-            return this.clear();
+            this.clearHints();
         }
     }
 
-    clear() {
-        this.ctx.visibleRustEditors.forEach(it => {
-            this.setTypeDecorations(it, []);
-            this.setParameterDecorations(it, []);
-        });
+    clearHints() {
+        for (const file of this.sourceFiles) {
+            file.inlaysRequest?.cancel();
+            this.renderHints(file, []);
+        }
+    }
+
+    private renderHints(file: RustSourceFile, hints: ra.InlayHint[]) {
+        file.renderHints(hints, this.client.protocol2CodeConverter);
     }
 
-    async refresh() {
+    refreshRustDocument(document: RustTextDocument) {
         if (!this.enabled) return;
-        await Promise.all(this.ctx.visibleRustEditors.map(it => this.refreshEditor(it)));
-    }
-
-    private async refreshEditor(editor: vscode.TextEditor): Promise<void> {
-        const newHints = await this.queryHints(editor.document.uri.toString());
-        if (newHints == null) return;
-
-        const newTypeDecorations = newHints
-            .filter(hint => hint.kind === ra.InlayKind.TypeHint)
-            .map(hint => ({
-                range: this.ctx.client.protocol2CodeConverter.asRange(hint.range),
-                renderOptions: {
-                    after: {
-                        contentText: `: ${hint.label}`,
-                    },
-                },
-            }));
-        this.setTypeDecorations(editor, newTypeDecorations);
-
-        const newParameterDecorations = newHints
-            .filter(hint => hint.kind === ra.InlayKind.ParameterHint)
-            .map(hint => ({
-                range: this.ctx.client.protocol2CodeConverter.asRange(hint.range),
-                renderOptions: {
-                    before: {
-                        contentText: `${hint.label}: `,
-                    },
-                },
-            }));
-        this.setParameterDecorations(editor, newParameterDecorations);
-    }
-
-    private setTypeDecorations(
-        editor: vscode.TextEditor,
-        decorations: vscode.DecorationOptions[],
-    ) {
-        editor.setDecorations(
-            typeHintDecorationType,
-            this.enabled ? decorations : [],
-        );
-    }
-
-    private setParameterDecorations(
-        editor: vscode.TextEditor,
-        decorations: vscode.DecorationOptions[],
-    ) {
-        editor.setDecorations(
-            parameterHintDecorationType,
-            this.enabled ? decorations : [],
-        );
-    }
-
-    private async queryHints(documentUri: string): Promise<ra.InlayHint[] | null> {
-        this.pending.get(documentUri)?.cancel();
 
-        const tokenSource = new vscode.CancellationTokenSource();
-        this.pending.set(documentUri, tokenSource);
+        const file = this.sourceFiles.getSourceFile(document.uri.toString());
+
+        assert(!!file, "Document must be opened in some text editor!");
+
+        void file.fetchAndRenderHints(this.client);
+    }
+
+    refreshVisibleRustEditors(visibleEditors: RustTextEditor[]) {
+        if (!this.enabled) return;
+
+        const visibleSourceFiles = this.sourceFiles.drainEditors(visibleEditors);
 
-        const request = { textDocument: { uri: documentUri } };
+        // Cancel requests for source files whose editors were disposed (leftovers after drain).
+        for (const { inlaysRequest } of this.sourceFiles) inlaysRequest?.cancel();
 
-        return sendRequestWithRetry(this.ctx.client, ra.inlayHints, request, tokenSource.token)
-            .catch(_ => null)
-            .finally(() => {
-                if (!tokenSource.token.isCancellationRequested) {
-                    this.pending.delete(documentUri);
+        this.sourceFiles = visibleSourceFiles;
+
+        for (const file of this.sourceFiles) {
+            if (!file.rerenderHints()) {
+                void file.fetchAndRenderHints(this.client);
+            }
+        }
+    }
+}
+
+
+/**
+ * This class encapsulates a map of file uris to respective inlay hints
+ * request cancellation token source (cts) and an array of editors.
+ * E.g.
+ * ```
+ * {
+ *    file1.rs -> (cts, (typeDecor, paramDecor), [editor1, editor2])
+ *                  ^-- there is a cts to cancel the in-flight request
+ *    file2.rs -> (cts, null, [editor3])
+ *                       ^-- no decorations are applied to this source file yet
+ *    file3.rs -> (null, (typeDecor, paramDecor), [editor4])
+ * }                ^-- there is no inflight request
+ * ```
+ *
+ * Invariants: each stored source file has at least 1 editor.
+ */
+class RustSourceFiles {
+    private files = new Map<string, RustSourceFile>();
+
+    /**
+     * Removes `editors` from `this` source files and puts them into a returned
+     * source files object. cts and decorations are moved to the returned source files.
+     */
+    drainEditors(editors: RustTextEditor[]): RustSourceFiles {
+        const result = new RustSourceFiles;
+
+        for (const editor of editors) {
+            const oldFile = this.removeEditor(editor);
+            const newFile = result.addEditor(editor);
+
+            if (oldFile) newFile.stealCacheFrom(oldFile);
+        }
+
+        return result;
+    }
+
+    /**
+     * Remove the editor and if it was the only editor for a source file,
+     * the source file is removed altogether.
+     *
+     * @returns A reference to the source file for this editor or
+     *          null if no such source file was not found.
+     */
+    private removeEditor(editor: RustTextEditor): null | RustSourceFile {
+        const uri = editor.document.uri.toString();
+
+        const file = this.files.get(uri);
+        if (!file) return null;
+
+        const editorIndex = file.editors.findIndex(suspect => areEditorsEqual(suspect, editor));
+
+        if (editorIndex >= 0) {
+            file.editors.splice(editorIndex, 1);
+
+            if (file.editors.length === 0) this.files.delete(uri);
+        }
+
+        return file;
+    }
+
+    /**
+     * @returns A reference to an existing source file or newly created one for the editor.
+     */
+    private addEditor(editor: RustTextEditor): RustSourceFile {
+        const uri = editor.document.uri.toString();
+        const file = this.files.get(uri);
+
+        if (!file) {
+            const newFile = new RustSourceFile([editor]);
+            this.files.set(uri, newFile);
+            return newFile;
+        }
+
+        if (!file.editors.find(suspect => areEditorsEqual(suspect, editor))) {
+            file.editors.push(editor);
+        }
+        return file;
+    }
+
+    getSourceFile(uri: string): undefined | RustSourceFile {
+        return this.files.get(uri);
+    }
+
+    [Symbol.iterator](): IterableIterator<RustSourceFile> {
+        return this.files.values();
+    }
+}
+class RustSourceFile {
+    constructor(
+        /**
+         * Editors for this source file (one text document may be opened in multiple editors).
+         * We keep this just an array, because most of the time we have 1 editor for 1 source file.
+         */
+        readonly editors: RustTextEditor[],
+        /**
+         * Source of the token to cancel in-flight inlay hints request if any.
+         */
+        public inlaysRequest: null | vscode.CancellationTokenSource = null,
+
+        public decorations: null | {
+            type: vscode.DecorationOptions[];
+            param: vscode.DecorationOptions[];
+        } = null
+    ) { }
+
+    stealCacheFrom(other: RustSourceFile) {
+        if (other.inlaysRequest) this.inlaysRequest = other.inlaysRequest;
+        if (other.decorations) this.decorations = other.decorations;
+
+        other.inlaysRequest = null;
+        other.decorations = null;
+    }
+
+    rerenderHints(): boolean {
+        if (!this.decorations) return false;
+
+        for (const editor of this.editors) {
+            editor.setDecorations(typeHints.decorationType, this.decorations.type);
+            editor.setDecorations(paramHints.decorationType, this.decorations.param);
+        }
+        return true;
+    }
+
+    renderHints(hints: ra.InlayHint[], conv: lc.Protocol2CodeConverter) {
+        this.decorations = { type: [], param: [] };
+
+        for (const hint of hints) {
+            switch (hint.kind) {
+                case ra.InlayHint.Kind.TypeHint: {
+                    this.decorations.type.push(typeHints.toDecoration(hint, conv));
+                    continue;
+                }
+                case ra.InlayHint.Kind.ParamHint: {
+                    this.decorations.param.push(paramHints.toDecoration(hint, conv));
+                    continue;
                 }
-            });
+            }
+        }
+        this.rerenderHints();
+    }
+
+    async fetchAndRenderHints(client: lc.LanguageClient): Promise<void> {
+        this.inlaysRequest?.cancel();
+
+        const tokenSource = new vscode.CancellationTokenSource();
+        this.inlaysRequest = tokenSource;
+
+        const request = { textDocument: { uri: this.editors[0].document.uri.toString() } };
+
+        try {
+            const hints = await sendRequestWithRetry(client, ra.inlayHints, request, tokenSource.token);
+            this.renderHints(hints, client.protocol2CodeConverter);
+        } catch {
+            /* ignore */
+        } finally {
+            if (this.inlaysRequest === tokenSource) {
+                this.inlaysRequest = null;
+            }
+        }
     }
 }
+
+type RustTextDocument = vscode.TextDocument & { languageId: "rust" };
+type RustTextEditor = vscode.TextEditor & { document: RustTextDocument; id: string };
+
+function areEditorsEqual(a: RustTextEditor, b: RustTextEditor): boolean {
+    return a.id === b.id;
+}
+
+function isRustTextEditor(suspect: vscode.TextEditor & { id?: unknown }): suspect is RustTextEditor {
+    // Dirty hack, we need to access private vscode editor id,
+    // see https://github.com/microsoft/vscode/issues/91788
+    assert(
+        typeof suspect.id === "string",
+        "Private text editor id is no longer available, please update the workaround!"
+    );
+
+    return isRustTextDocument(suspect.document);
+}
+
+function isRustTextDocument(suspect: vscode.TextDocument): suspect is RustTextDocument {
+    return suspect.languageId === "rust";
+}
diff --git a/editors/code/src/rust-analyzer-api.ts b/editors/code/src/rust-analyzer-api.ts
index 6a7aeb602..bd6e3ada0 100644
--- a/editors/code/src/rust-analyzer-api.ts
+++ b/editors/code/src/rust-analyzer-api.ts
@@ -98,8 +98,8 @@ export namespace InlayHint {
         range: lc.Range;
         label: string;
     }
-    export type TypeHint = Common & { kind: Kind.TypeHint; }
-    export type ParamHint = Common & { kind: Kind.ParamHint; }
+    export type TypeHint = Common & { kind: Kind.TypeHint };
+    export type ParamHint = Common & { kind: Kind.ParamHint };
 }
 export interface InlayHintsParams {
     textDocument: lc.TextDocumentIdentifier;